1. Field of the Invention
The present invention relates to systems for communicating between application programs over a telecommunications network. More particularly, the present invention relates to application to application communication using a defined protocol such as TCP/IP between systems which may include high performance input/output mechanisms.
2. Background and Related Art
Data processing systems are used for a large number of functions in business, research and education. The computer systems used for these functions are frequently geographically dispersed, but required to be interlinked for certain purposes. This has led to the creation of telecommunication networks linking computer systems and the creation of telecommunications protocols to assist in the orderly communication between systems.
Data processing application programs used with distributed computer systems often employ the client-server model for network applications. In this model, one or more computer systems are designated as "servers" able to respond to requests from "clients" to perform various services. Server applications may provide functions such as printing, file storage, or processing resources. The server process is typically started in one computer system and is caused to wait and "listen" for a request by a client for service. Upon receipt of that request, the server wakes up and provides the requested service.
Communications between client and server applications take place according to a defined network protocol. A protocol is a set of rules and conventions used by the applications participating in a conversation. The set of rules can become very complex and layered protocol models have been adopted to help simplify and manage network protocol definitions. The International Standards Organization (ISO) has developed the Open Systems Interconnection Model (OSI) for computer communications. The OSI model consists of seven layers with well defined interfaces between the layers. Most computer network protocols are described in terms of the OSI model.
FIG. 1 presents an example of a network illustrating the seven layer OSI model. Two computer systems are shown 102 and 104. The systems are connected by a Local Area Network (LAN) 106. The OSI model is applicable not only to local area networks, typically connecting multiple computers within a building, but also to wide area networks (WANs) connecting computers in different cities or countries and to internetworks (Internet) connecting several physically separate networks (either LANs or WANs).
Application programs 108 and 110 communicate over LAN 106 via protocol processors 112 and 114. Protocol processors 112 and 114 are typically implemented as part of the operating system of the computer running the application program. The OSI protocol comprises the following seven layers: Application(7), Presentation(6), Session(5), Transport(4), Network(3), DataLink(2), and Physical(1). The higher layers 4-7 operate on messages. The network layer 3 typically operates on packets, the datalink layer 2 on frames, while the lowest level physical layer 1 operates on bits of data.
In this illustration each computer has identical software layers and each layer logically communicates to the same layer at the other computer, except for the presentation layer. The physical layer is the hardware interface adapter. This portion physically connects to the other computer and controls the signals on the communications media. The Data Link layer provides the hardware interface routines usually in terms of software. This layer generally handles the interrupts, framing and unframing. The Network layer provides internet routing or forwarding packets to other computers on the network. This is generally done with routing tables. The Transport layer provides the flow control, assembly and disassembly of data from one computer to another. This layer has the most overhead in the protocol stack. The Transport layer sends control messages as well as data packets. The Session layer is the interface to the application program. In terms of TCP/IP often layers 4 and 5 are discussed conceptually as a single layer, known as the Transport layer. Layer 6 is the presentation layer. This layer provides common routines for applications but doesn't communicate with its matching component on the destination computer. Layer 7 is the Applications layer. A file transfer program would be an example of an application.
Several network protocols have been defined and are in use in computer networks. These include TCP/IP, Systems Network Architecture (SNA), and NetBios. The low level physical connection can operate on known technologies such as Ethernet, Token Ring, or long distance networks provided by the telephone companies.
The TCP/IP protocol was defined by the U.S. government and is used to link many research and educational institutions that perform work for the government. Its widespread use has resulted in many other companies adopting TCP/IP to be able to communicate with existing TCP/IP sites. Although developed before the OSI model, TCP/IP components can be mapped to the seven layer model. The TCP/IP "process" layer encompasses OSI Presentation and Session layers. Two Transport layers are defined, Transmission Control Protocol (TCP) which provides a connection based protocol, and the User Datagram Protocol (UDP) which provides a connection-less protocol. Internet Protocol (IP) provides the Network layer for both TCP and UDP while the DataLink layer is met by the appropriate hardware interface.
Returning to FIG. 1, application program 108 communicates via the network using an Application programming interface (API). The sockets protocol is one of the more prevalent application to application APIs. The sockets API was developed for use on Digital Equipment Corporation (DEC) VAX computers (DEC and VAX are trademarks of Digital Equipment Corp.) by the University of California, Berkeley, as the BSD operating system, a derivative of the UNIX operating system. (UNIX is a trademark of Unix System Laboratories.) The sockets API defines the format and parameter content of the commands an application program uses to establish communications with another application. It defines the API for both client and server applications and for connection-less and connection-based links. The defined API functions cause the operating system to issue the necessary commands to establish a communications link and to exchange data over that link.
The sockets API has been implemented on a variety of computer systems from small microcomputers to large mainframes. The sockets API has been implemented on IBM ES/9000 mainframes (IBM and ES/9000 are trademarks of the IBM Corp.) to provide network connectivity to programs running on those systems. This implementation has not been without problems, however, due to the differences in hardware architectures between the IBM ES/9000 computer and the DEC VAX computer for which the sockets API was originally developed. IBM ES/9000 computers and other "mainframe" computers typically are capable of processing a large number of programs and provide very high speed input output (I/O) capabilities. High speed I/O is necessary to provide the great throughput characteristic of mainframe computers. I/O is typically implemented as I/O Channels on these systems, with the channels having the ability to transfer data into or out of the system without intervention from the main processor. Channels can transfer several hundred megabytes of data per second using data streaming techniques. Most LANs, WANs, and telecommunication networks, however, are more limited and transfer only a few kilobytes to at most five megabytes per second. This data transfer mismatch results in undesirable mainframe network performance when implementing protocols such as TCP/IP.
FIG. 2 illustrates a prior art configuration for the connection of an IBM ES/9000 processor (having a System/370 or System/390 architecture) to a local area network. (System/370 and System/390 are trademarks of IBM Corp.) Processor 202 is connected through its channel 204 to a control unit 206 that is connected to the LAN 208. The protocol processor in processor 202 performs all of the network protocol functions such as formatting messages for transmission over the LAN. Control unit 206 accepts the transmission packets in physical adapter 212 which is adapted for channel attachment and the receipt of high volumes of data, and places the packets on the LAN via physical adapter 214 that is adapted to attach to a network. The opposite flow takes place for packets received from the LAN.
The processor 202 thus spends considerable processing time handling the routine network tasks in protocol processor section, and is generally unable to take advantage of the high speed I/O capabilities because of the limited receiving abilities of LAN 208. The processing time spent in these network tasks is therefore unavailable for more productive processing thereby reducing the overall effectiveness of the processor 202.
A technical problem of improving the performance of large computer systems when engaging in network communications using standard protocols is therefore presented.